Towing and Hot AT

[Travelator Lurker Find all posts View Profile Close Travelator]

I have recently done a several thousand km trip towing a caravan with a GVM below 1500kg. The majority of the trip was uneventful but there were a few hill climbs that gave me some grief.

The most recent climb was the Cunningham gap (between Brisbane and Warwick) with the temperature in the mid 30's. The AC was off and I was driving at around 60km/h in 3rd or 2nd with the revs around 2,500-3,000. The temp gauge was high and near the top, got very close to the red band. The AT Tenp light came on during the last kilometre and so I stopped at the top until gone.

I have had the AT Temp light come one before at the end of a climb but not seen the engine temperature so high.

The van is we'll below the Prado's limit and I'm wondering why it struggles so much. I am thinking about installing a transmission cooler to help.

Any advice please on what I can do to help the Prado and transmission run cooler?

[gspy4u Senior Member Find all posts View Profile Close gspy4u]

We tow a a tandem axle over 2T and have never had a temp problem. Ours is manual though but engines temp has never gone up enough to notice or worry about no matter how big or long a hill it was. Have done Cunninghams many times no problem.
Need more info, age of vehicle, how many k's ? etc

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey Travelator,

Auto transmissions (on any vehicle) work very hard when towing, or driving in sand etc.

The issue in the Prado is the transmission fluid runs through the radiator to help heat the transmission oil up to temperature. This means if the engine runs hot, the radiator fluid runs hot, and subsequently the transmission oil gets hotter.

It's obviously not the greatest setup in the world. You can replace the small OEM transmission cooler at the front with a larger cooler (Davies Craig for instance), and this can lower operating temps significantly.

I would also invest in a scanguage so you can monitor the radiator temperature and the transmission temperature.

You may have also cooked your transmission oil, so give it a flush as well.

Hope you get it sorted!

Best

Mark

[Travelator Lurker Find all posts View Profile Close Travelator]

Thanks whitey.

Pretty sure I will replace the cooler. Unfortunately the scangauge is not compatible with the 4 speed manual according to their website. Are there any other similar units that would be compatible?

[red hilux Member Find all posts View Profile Close red hilux]

Thanks whitey.
Unfortunately the scangauge is not compatible with the 4 speed manual according to their website.

http://scangauge.com.au/compatibility-toyota/

that suks

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

Hey Travelator,

Auto transmissions (on any vehicle) work very hard when towing, or driving in sand etc.

The issue in the Prado is the transmission fluid runs through the radiator to help heat the transmission oil up to temperature. This means if the engine runs hot, the radiator fluid runs hot, and subsequently the transmission oil gets hotter.

It's obviously not the greatest setup in the world. You can replace the small OEM transmission cooler at the front with a larger cooler (Davies Craig for instance), and this can lower operating temps significantly.

I would also invest in a scanguage so you can monitor the radiator temperature and the transmission temperature.

You may have also cooked your transmission oil, so give it a flush as well.

Hope you get it sorted!

Best

Mark

Hey Mark
That's not quite the whole story regarding heating the trans oil, lets call it regulating the temp of the trans oil. Towing or working the torque converter hard will heat the oil past the temperature of the radiator coolant and in that situation the oil will pass heat into the coolant to be dissipated by the radiator. I'm not saying adding an external cooler isn't advantageous of course.

Cheers

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

http://scangauge.com.au/compatibility-toyota/

that suks

Show me a Prado with a 4 speed manual..

[Travelator Lurker Find all posts View Profile Close Travelator]

Show me a Prado with a 4 speed manual..

Oops. Typo. Meant the 4 speed auto.

[adrian5800 Advanced Member Find all posts View Profile Close adrian5800]

Oops. Typo. Meant the 4 speed auto.

Get a bluetooth OBD dongle and an android device with the Torque app, follow the guide on this thread and have trans temps as a gauge on Torque.
http://www.pradopoint.com/showthread...n-M-OBD-Prados

[Travelator Lurker Find all posts View Profile Close Travelator]

Brilliant. Thanks for that.

[Brett1979 Avid PP Poster! Find all posts View Profile Close Brett1979]

If your radiator overheated towing a 1.5T van up a hill then I don't think it's running at full efficiency and has shown the early signs of a partial blockage because the overheating is not normal. This is how it starts, but of course towing will expose this issue earlier than not towing. All of your transmission fluid will also be pumped through a small section of the radiator within a minute or so when driving to help keep it cool. If your radiator overheated then it'll cook your trans fluid too on a hot day. I'd replace your radiator which I think will fix your engine overheating problem from happening again. It may even have the front of the fins blocked up with bugs or something so check that first.

As for the transmission over heating on its own, towing is stressful and will do this once in a blue moon if the conditions allow. But overheating the radiator coolant is not normal and look into fixing that. The Prado petrol engines are highly resilient and will put up with overheating on more than a few occasions, but there will be that one time where it'll breakdown a gasket enough to form an oil leak, or you can warp your head causing an internal coolant leak.

[Travelator Lurker Find all posts View Profile Close Travelator]

Thanks Brett.

I had the radiator replaced around 12 months ago as there was some cracking found. The radiator didn't actually overheat but the needle got pretty close to the red band. The transmission did overheat (according to the cluster light!). This was the first time that I have seen the radiator temp this high. The last time that I got the AT Temp light on the radiator temp was around the 3/4 position and normal driving/towing it sits at around the 1/2 mark.

I think I will take it to my local bloke and have it investigated. Hoping to grab a bigger van in the future (kids growing and need more room) but if she can't handle 1.5 tonnes then I may have to look at disposing the Prado.

[Brett1979 Avid PP Poster! Find all posts View Profile Close Brett1979]

Im unsure if the 120 is similar, but the 90 series temp gauge is not to scale. By this I mean that if it reaches 3/4 it's overheated and any higher will have the coolant bubbling like mad. The boiling point of properly mixed coolant is between 127 and 132 degrees. If it nearly reaches the red it's dangerously high. If you go up to or over the red then you're at real risk of doing damage to the engine. But like I said, I unsure if your temp scale is also not really to scale. Your car should be able to pull a 1.5T van no probs without risk of overheating unless you're trying to flog your car hard up a really long steep hill on a hot day, which you weren't doing going by your description. My father-in-law has pulled a 1.5T van with his 4 cyl petrol X-Trail for years all over the country and never over heated anything once. I would've heard about it if he did because I service his car for him. Cunninghams Gap shouldn't be pushing your cooling system to its limit as its not that steep. There is something wrong effecting coolant flow and if you decide to get a bigger van as you plan to do you'll overheat a whole lot more as you can imagine every time you hit a lengthy incline which is far from normal. I don't want you to spend money unnecessarily and it'd be handy if you can check and work on things yourself as it'll save you a fair bit of money, but Im wondering if your water pump isn't working as it should. If you have the know how to replace it yourself it'll only cost you $100 for an after market water pump plus an extra $35 for a tube of Toyota gasket sealant (FIPG) which is excellent stuff. Something's not right though. Imagine if you towed a loaded up camper trailer on Fraser Island, you'd be overheating there too driving into a head wind on the beach or driving in soft sand on a hot day with deflated tyres.

Since your radiator was replaced a year ago I'm assuming it's in perfect working order and also assuming the thermostat ($30 part) was replaced at the same time and also in perfect working order. The only other thing that would really come into question now is the water pump. Do you having anything covering the front of your radiator like a bug mesh of some type? And this is an important one, did you ever use "stop leak" to try and fix the cracked radiator issue? That stuff can screw with your cooling system down the track. Also did you ever add a fair bit of tap water to your cooling system during the earlier stages of losing coolant when you had the crack? Tap water added to the cooling system will corrode the metal spindle of the water pump. I've see this a few times. If you added tap water for sometime my bet is a bit of your water pump spindle had corroded and hence your problem. Must use coolant and demineralized water only or the spindle will start rusting away. Dont ever add tap water unless you plan on replacing your water pump down the track anyway.

I'd get to the bottom of this issue though before you upgrade your van as it'd be bloody annoying every time you encounter a long hill. To me, it'd be better to diagnose and fix this coolant temp problem then replace the car. Check your trans fluid too. If it smells burnt on the dip stick, replace it. There may be another PP member close to you in Brissy with the know how that would happily help you out with showing you how to replace trans fluid if you're unsure. They may also lend most of their day to helping you swap out your water pump as a process of elimination. The Toyota FIPG can be used on a water pump in a car being driven only a short while after. It's what the Toyota mechanics use.

[Whitey Shockie Maker of the Month Award Find all posts View Profile Close Whitey]

Hey all,

I have recently read on fjcc that the at temp light comes on at 150C and will stay on until it has cooled back past 135C, see here, post #20;

http://www.fjcc.com.au/f37/t-temp-li...23/index2.html

The FJ uses the same A750F transmission.

I also spoke with Penrite today about their ATF LV...actually my good mate Chris from fjcc spoke with them and all the info was relayed to me.

Note that the Penrite ATF LV has been designed to be the equivalent of Toyota WS fluid.

Penrite ATF LV

40C 28
100C 5.7
Flashpoint 219C
density 0.846

Toyota WS

40C 24
100C 5.4
Flashpoint 194C
density 0.854

Penrite state that the atf should not be run past 100C. Run the fluid to 150C and you can measure the lifetime of the auto in hundreds of km's. Hit 200C and it's a dead box. There is a thread on fjcc where an owner has had to replace his torque converter after the at temp light has come on, $3500 bill.

I have seen 115C-120C on my transmission in soft sand with a loaded up Prado on several occasions, and I have had to back off. Mine is a petrol with the OEM cooler. Locking the centre diff in soft sand will push the temps right up.

Today I went out and bought a 30 plate Davies Craig 679 cooler, which should drop the running temps by around 20C.

50-80C is apparently the optimal running temperature for the auto.

Best

Mark

[Travelator Lurker Find all posts View Profile Close Travelator]

Thanks Brett.

The crack in the radiator was picked up during a service. I never added any "stop leak" or tap water. The crack was not significant enough to lose too much fluid. I have only ever had coolant in the system (as long as I have had this vehicle anyway).

Thanks for the insight Mark. Pretty concerned about the health of my gearbox now! I am taking it to my mechanic (very trusted) in the morning and we are going to see if we can find the problem, looking at the fan, water pumps radiator etc. I will also dump the ATF and cross my fingers that its not too bad.